The propagation and the gate operation of femtosecond pulses in nonlinear optical waveguides utilizing the saturation of the intersubband absorption at 1.55 µm in nitride multiple quantum wells are simulated for the first time. The calculation was carried out by a one-dimensional finite-difference time-domain (FD-TD) method combined with three-level rate equations describing the intersubband carrier dynamics. The absorption recovers within 1 ps when the pulse width is less than 200 fs, which will allow 1-Tb/s operation. However, the pulse shape may be deformed with the propagation due to the coherent effect and the interference between the signal and the control pulses, and thus, optimization of the pulse widths and the incident timing is required. Since the transparent window (width of the control pulse) becomes shorter according to the propagation, the width of the control pulse should be set broader than that of the signal pulse. As an example, we assume the case where a 1.6-µm, 100-fs signal pulse is gated by a 300-fs control pulse at a wavelength of 1.5 µm in a 500-µm length waveguide. A 140-fs gated signal pulse with a smooth envelope is expected to appear after the band-pass filter. The extinction ratio is expected to be greater than 15 dB.

1.5 µm-band LiNbO3 quasiphase matched (QPM) wavelength converters consisting of a periodical domain inverted structure and a proton exchanged waveguide, have been studied in detail both theoretically and experimentally. Optimum device fabrication conditions are investigated with respected to waveguide propagation loss, coupling loss to a single-mode fiber and wavelength conversion efficiency. A normalized conversion efficiency as high as 200 %/W (by a SHG measurement) and a fiber-to-fiber insertion loss of less than 3.5 dB (@1.55 µm) is obtained for a wavelength converter module with a device length of 40 mm. It is shown that a highly uniform periodical domain inverted structure and a uniform proton exchange waveguide are key to obtaining efficient wavelength conversion. The tolerance of the waveguide width fluctuation is found to be very critical and is less than 20 nm for a 40 mm-long device. Future optimization of LiNbO3 QPM wavelength converters and the possible device applications in future optical communication systems are also presented.

A new algorithm is proposed for improving the convergence of backpropagtion networks. This algorithm is obtained by combining the conjugate gradient method and the Kalman filter algorithm. Simulation results show that the proposed algorithm can perform satisfactorily in all cases considered.

Simultaneous wavelength conversion of multi-WDM channels is expected to be a key technique in near-future networks. In this paper, 4-channel wavelength conversion using four-wave mixing (FWM) in a hybrid wavelength selector is successfully demonstrated. The wavelength selector consists of two four-channel spot-size-converter-integrated semiconductor optical amplifier (SS-SOA) gate arrays on a planar-lightwave-circuit (PLC) platform and two PLC-arrayed-waveguide-gratings (AWGs). As the wavelength selector has an individual SS-SOA for the wavelength conversion of each channel, there is negligible interference between channels. Four WDM channels with an 2.5 Gb/s modulation were converted from 1555 to 1575 nm. Clear eye openings and only a small power penalty of less than 0.5 dB were observed. The receiver sensitivity was -31 dBm at a bit error rate (BER) of 10-9.

An analytical error characteristics of GPS compass which determines heading and elevation of the vehicle using carrier phase measurements from 2 antennae is given. It is also shown that to obtain more precise heading, longer baseline along the vehicle is preferred and the accuracy of heading is always better than that of elevation since the vertical measurement uncertainty caused by geometry of satellites affects only on that of elevation. These results can be applied as basic directions for attitude determination: to what direction should the baseline be located to minimize the error, which satellites should be selected to minimize the error.

HRTFs (head-related transfer functions) are available for sound field reproduction with spatial fidelity, since HRTFs involve the acoustic cues such as interaural time difference, interaural intensity difference and spectral cues that are used for the perception of the location of a sound image. Generally, FIR filters are used in the simulation of HRTFs. However, this method is not useful for a simply system, since the orders of the FIR filters are high. In this paper, we propose a method using IIR filter for simply realization of sound image localization. The HRTFs of a dummy-head were approximated by the following filters: (A) fourth to seventh-order IIR filters and (B) third-order IIR filters. In total, the HRTFs of 24 different directions on the horizontal plane were used as the target characteristics. Sound localization experiments for the direction and the elevation angle of a sound image were carried out for 3 subjects in a soundproof chamber. The binaural signal sounds using the HRTFs simulated by FIR filters and approximated by IIR filters (A) and (B) were reproduced via two loudspeakers, and sound image localization on the horizontal plane was realized. As the result of the experiments, the sound image localization using the HRTFs approximated by IIR filters (A) is the same accuracy as the case of using the FIR filters. This result shows that it is possible to create sound fields with binaural reproduction more simply.

A simple phase compensation technique with improved power supply rejection ratio (PSRR) for CMOS opamps is proposed. This technique is based on feeding back a current proportional to a derivative of the voltage difference between an output and an input, and does not require a common-gate circuit or a noise-free bias for the circuit. The proposed technique requires only two additional transistors, which are connected to the differential pair of transistors in a cascade manner, and the compensation capacitor is connected to the source node of the additional transistor. Experimental results show an improvement of more than 20 dB in the PSRR at high frequencies, comparing the technique with a Miller compensation. This technique also improves the unity gain frequency and the phase margin from 0.9 MHz and 17 to 1.8 MHz and 44 for 200 pF load capacitance, respectively.

Today's market share of Intelligent Network (IN) service is growing rapidly in wireless networks due to the rapid advances in wireless telecommunication and IN technology. To guarantee network independent IN services, mobility of IN service subscribers has to be taken into account. This paper proposes new designs of Global Service Logic for the IN service enhancement, which increase call completion rates in wired and wireless intelligent networks. In order to apply this logic to wireless service subscribers as well as wired service subscribers, we implement a Queue Manager applied to the call queuing service feature in the Service Control Point (SCP). In the case of wireless service subscribers, the Home Location Register (HLR) handles the service registration flags to notify the Queue Manager of the corresponding service subscribers' mobility. In addition, we present a dynamic queue management mechanism, which dynamically manages the queue size based on the parallel server queuing model as the wireless subscribers roam the service groups due to their mobility characteristics. In order to determine the queue size allocated by the dynamic queue manager, we simulate the relationship between the number of the subscriber's terminals and the drop rate by considering the service increment rate. Moreover, the appropriate waiting time in the queue as required is simulated according to the above relationship. We evaluate call completion rates of the proposed mechanism in the paper by comparing to that of the existing mechanism.

This paper proposes a survivor-correction Viterbi algorithm (SCVA) and presents its application to an iterative sequence estimation in order to improve bit error rate performance of decision-feedback sequence estimation (DFSE) in the presence of intersymbol interference. The SCVA can mitigate erroneous survivor selections due to DFSE, because it modifies the add-compare-select operation to an add-correct-compare-select operation. Finally, it is confirmed by computer simulation that complexity of the proposed scheme is independent of delay of the main delayed ray and its performance is superior to that of DFSE at the same number of states.

The essence of this work is to introduce an interaction between the physical layer and higher network layers, thus enabling a more practical utilization of multiuser detection and supporting services with different QoS parameters. In this paper, a new hybrid TDMA/ Multicode (MC)-CDMA medium access control utilizing multiuser detection is proposed and analyzed. Further, two traffic flow control approaches accompanied the TDMA/MC-CDMA system are proposed. One approach deterministically controls the flow of traffic into the TDMA slots, while the other statistically controls the flow of traffic depending on the instantaneous changes in the traffic load. The two approaches have been examined under a wide range of traffic characteristics where AWGN is only considered besides the mutual interferers from other intracell users. Both approaches show superiority as well as less sensitivity in terms of BER to the traffic changes compared with the conventional system.

Software radio or software defined radio (SDR) is a quite attractive field of research in terms of theoretical cross-over research themes between radio engineering and computer science in academia as well as new multi-standard or all-purpose radio system products in industry. In order to promote research and development in a field of SDR this paper briefly introduces some prospective aspect and research themes on SDR. There are many approaches to research SDR such as architectures, devises, algorithms, description languages and API (application program interface) for achieving reconfigurability and downloadability in an SDR system. One of the approaches is to focus on an antenna for SDR. Although a baseband circuit is generally programable and reconfigurable, an antenna and a RF circuit are used to be less flexible and hardware-dependent and then result in a bottleneck for implementing an SDR system. However, an adaptive array antenna or a smart antenna named a software antenna is adaptively controllable and reconfigurable because it can be programable to form a desired beam pattern if an appropriate set of antenna weights is provided with software. It must be a vital tool for carrying out an SDR system. A software antenna can be considered as an adaptive filter in space and time domains for radio communications, so that the communication theory can be generalized from a conventional time domain into both space and time domains. This paper also introduces structures and theories of a software antenna which I have been studying before this millennium.

This paper reports the prehistory of software defined radio (SDR) studies in Japan. In 1999, a boom in the field of SDR started in Japan, and this year an ARIB study group completed its final report on SDR. SDR is a recently proposed technology concept and has attracted the attention of many communication engineering researchers. SDR will become one of the most important technologies in advanced communication, broadcasting and intelligent transportation systems on the 21st century. Although SDR has several attractive features, there are also many design issues to be solved. In this work we have examined these issues and discussed a new design methodology for wireless receivers in the SDR era.

In this paper, we study efficient scheduling algorithms that are suitable for ATM networks. In ATM networks, all packets have a fixed small length of 53 bytes and they are transmitted at very high rate. Thus time complexity of a scheduling algorithm is quite important. Most scheduling algorithms proposed so far have a complexity of O(log N) per packet, where N denotes the number of connections sharing the link. In contrast, weighted round robin (WRR) has the advantage of having O(1) complexity; however, it is known that its delay property gets worse as N increases. To solve this problem, in this paper we propose two new variants of WRR, uniform round robin (URR) and idling uniform round robin (I-URR). Both disciplines provide end-to-end delay and fairness bounds which are independent of N. Complexity of URR, however, slightly increases as N increases, while I-URR has complexity of O(1) per packet. I-URR also works as a traffic shaper, so that it can significantly alleviate congestion on the network. We also introduce a hierarchical WRR discipline (H-WRR) which consists of different WRR servers using I-URR as the root server. H-WRR efficiently accommodates both guaranteed and best-effort connections, while maintaining O(1) complexity per packet. If several connections are reserving the same bandwidth, H-WRR provides them with delay bounds that are close to those of weighted fair queueing.

In this paper we propose a new lattice based second-order adaptive infinite impulse response (IIR) notch filter that uses a simplified adaptation algorithm. Steady-state analysis of the proposed structure is then studied based on the mean-squared error analysis of the steady-state variable coefficient fluctuations. The analysis is used to derive simple analytical expressions for steady-state variable coefficient variance and an upper bound for the step size adaptation constant. The results are shown to be useful in designing an FSK demodulator using the proposed structure. Computer simulation results are shown to confirm derived analytical expressions.

We propose here a time-domain shooting algorithm for calculating the steady-state responses of nonlinear RF circuits containing parasitic elements that is based on both a modified Newton and a secant methods. Bipolar transistors and MOSFETs in ICs have small parasitic capacitors among their terminals. We can not neglect them because they will gives large effects to the shooting algorithm at the high frequency. Since our purpose is to develop a user friendly simulator, we mainly take into account the relatively large normal capacitors such as coupling and/or by-pass capacitors and so on, because the parasitic capacitors are usually smaller and contained in the device models. We have developed a very simple simulator only using the fundamental tools of SPICE, which can be applied to relatively large scale ICs, efficiently.

This paper presents the effect of stress on device degradation in metal-oxide-semiconductor field-effect transistors (MOSFETs) due to stud bumping. Stud bumping above the MOSFET region generates interface traps at the Si/SiO2 interface and results in the degradation of transconductance in N-channel MOSFETs. The interface traps are apparently eliminated by both nitrogen and hydrogen annealing. However, the hot-carrier immunity after hydrogen annealing is one order of magnitude stronger than that after nitrogen annealing. This effect is explained by the termination of dangling bonds with hydrogen atoms.

The SDP (Sum of Disjoint Products) approach is a well-known technique for computing network reliability measures. So far several algorithms have been developed based on this approach. In this letter, we present a general framework for parallelization of these SDP algorithms. Based on the framework, we implemented a parallel version of an SDP algorithm called CAREL on a network of workstations. Experimental results show that it works fairly well with almost linear speedups.

This paper studies mutually coupled integrate-and-fire type chaotic oscillators. The coupling is realized by impulsive switchings and the system exhibits various synchronous and asynchronous phenomena. We give a basic classification of the chaos synchronization phenomena and their breakdown patterns. The stability of the synchronous states can be confirmed using the piecewise exact solutions, and the basic mechanism of the phenomena can be elucidated by a simple geometric consideration. The typical phenomena are confirmed in the laboratory.

The present paper modifies the algorithm to estimate harmful event frequencies and examines the definition of modes of operation in IEC 61508. As far as the continuous mode concerns, the calculated results coincide with those obtained based on the standard. However, for the intermediate region of medium demand frequencies and/or medium demand durations, the standard gives much higher harmful event frequencies than the real values. In order to avoid this difficulty, a new definition of modes of operation and a shortcut method for allocation of SILs are presented.

This paper describes a crossbar-switch arbiter for a high-speed MAPOS switch. The arbiter uses the following techniques suitable for variable-length frame switching: 1. parallel processing for handling requests from network interfaces and for resource allocation, 2. techniques such as release-on-request, fast back-to-back transfer, and request prefetching to reduce the arbitration overhead, and 3. a resource sampling technique to enable efficient one-shot multicast processing. Our simulation-based performance evaluation and estimation of the scale of its logic circuits indicated that this arbiter can be implemented through simple hardware.